Hydraulic driving device for bending presses

ABSTRACT

THE HYDRAULIC SYSTEM FOR A HYDRAULIC DRIVING DEVICE OF A BENDING PRESS INCLUDES TWO HYDRAULIC CONTROL CYLINDERS WHICH CO-OPERATE WITH THE UPPER JAW TO EFFECT VERTICAL RECIPROCATION OF THE UPPER JAW BETWEEN GUIDES THEREFOR. THE INVENTION PROVIDES FOR THE INCLUSION IN THE HYDRAULIC SYSTEM OF COMPENSATING CYLINDERS ASSOCIATED WITH THE CONTROL CYLINDERS AND HOUSING PISTONS HAVING OPERA-   TIVE SURFACE OF EQUAL AREA AND WHICH BY CO-OPERATION WITH THE CONTROL CYLINDERS PREVENT JAMMING OF THE UPPER JAW IN THE GUIDES DURING RECIPROCATION OF THE UPPER JAW.

G. cos'rA 3,613,355

HYDRAULIC DRIVING DEVICE FOR BENDING PRESSES Oct. 19, 1971 Filed March 25 1970 5 Sheets-Sheet 1 rlllll' Oct. 19, 1971 s. cosTA 3,613,365

HYDRAULIC DRIVING DEVICE FOR BENDING PRESSES Filed March 25, 1970 5 Sheets-Shoot 2 Oct. 19, 1971 G. COSTA HYDRAULIC DRIVING DEVICE FOR BENDING PRESSES 5 Sheets-Sheet 3 206 ca. COSTA 3,613,355

HYDRAULIC DRIVING DEVICE FOR BENDING PRESSES Oct. 19, 1971 5 Sheets-Sheet 8 Filed March 25, 1970 v 0 0 H H 7 m/J m ZJ 4 lllvfiro g T 6 60 m 92 J B 2 HR T m 5 h m a 3 B llv M w 4 u Q A R F11 z\ m O 11.. A J g i VA I ZJ T a I 2 a If a F 4 L w w r [A T1 I\ 3 A Y M 6 T W L V V r. w m, w 2 L|L 7 O 2H T 7L 6 0 2 6 H 7 2 0 0 h I 2 3 2 H 0 6 4| .4v 3.7 0 2 0 0 q R h 2 2 2 0 7 L I 2 0 0 0 Q l ..I.. 2 A 2 w United States Patent O 3,613,365 HYDRAULIC DRHVHNG DEVECE FOR BENDING PRESSES Giuseppe Costa, Genoa, Italy, assignor to Verrina S.p.A., Geneva-Voltri, Italy Filed Mar. 25, 1970, Ser. No. 22,605 Claims priority, application Italy, Mar. 29, 1969,

Int. Cl. FlSb 11/22 U.S. Cl. 60-52 HP Claims ABSTRACT OF THE DISCLOSURE The hydraulic system for a hydraulic driving device of a bending press includes two hydraulic control cylinders which co-operate with the upper jaw to effect vertical reciprocation of the upper jaw between guides therefor. The invention provides for the inclusion in the hydraulic system of compensating cylinders associated with the control cylinders and housing pistons having operative surface of equal area and which by co-operation with the control cylinders prevent jamming of the upper jaw in the guides during reciprocation of the upper jaw.

This invention relates to a hydraulic driving device for bending or like presses the hydraulic system of which includes a vertically reciprocable upper jaw and two hydraulic control cylinders disposed in spaced relation and arranged simultaneously to be acted upon by pressure to effect lowering and raising of the upper jaw.

It is an object of the invention to create a hydraulic driving device of the above mentioned kind, which is arranged automatically to assure a precise parallel displacement of the upper jaw, i.e. to prevent undesirable oblique positions of the upper jaw and jamming thereof in guides therefor.

The hydraulic driving device according to the invention is characterised by two compensating cylinders each housing a compensating piston, said piston being firmly interconnected and on sides thereof facing in the same direction having surfaces of equal area to be acted upon by pressure, the compensating cylinder spaces on one side of the compensating pistons each being connected to the pressure space of a displacing or control cylinder and the compensating cylinder spaces at the opposite sides of the compensating pistons being arranged to be acted upon by the same hydraulic counter-pressure or impelling pressure.

When the upper jaw moves in the direction opposed to the operating direction of the two control cylinders, e.g. under the action of two other hydraulic cylinders or the like, the hydraulic oil or fluid is displaced from the pressure spaces of the control or displacing cylinders and is forced into the pressure transmission spaces of the two compensating cylinders connected to them. The pair of compensating pistons is accordingly displaced against the hydraulic back pressure maintained in the control spaces of the compensating cylinders. If the one lateral extremity of the upper jaw is concomitantly decelerated more powerfully by an increased outer mechanical resistance, the hydraulic pressure diminishes in the pressure space of the co-ordinated displacing cylinder and in the pressure transmission space of the compensating cylinder connected thereto, whereas the hydraulic pressure rises to the same degree in the pressure tnansmission space of the other compensating cylinder and in the pressure space of the other displacing cylinder connected thereto, and accordingly opposes an increased hydraulic resistance to the co-ordinated lateral extremity of the upper jaw which is less powerfully decelerated by the outer mechanical resistance. The total resistances acting on the two extremities of the upper jaw are thus balanced with each other Patented Oct. 19, 1971 automatically and the upper jaw is accordingly guided precisely parallel to itself.

If the upper jaw is to be displaced in the opposite direction, i.e. in the operating direction of the two displacing cylinders, a sufficient impelling pressure is built up in the control or actuating spaces of the two compensating cylinders, which correlatively displaces the pair of compensating pistons. The hydraulic oil thereby displaced from the pressure transmission spaces of the compensating cylinders is forced into the pressure spaces of the two displacing cylinders and these engender the displacement of the upper jaw. If, in this case, the one lateral extremity of the upper jaw must overcome an increased external mechanical resistance, the hydraulic pressure in the pressure space of the co-ordinated displacing cylinder and in the pressure transmission space of the compensating cylinder connected thereto increases correlatively, whereas the hydraulic pressure in the pressure transmission space of the other compensating cylinder and in the pressure space of the other displacing cylinder connected thereto, decreases in the same degree. The displacing pressures acting on the two extremities of the upper jaw consequently adapt themselves to the outer resistances to be overcome by the co-ordinated extremities of the upper jaw automatically, so that oblique positions and jamming of the upper jaw are also prevented in this case.

The displacing cylinders of the upper jaw connected to the compensating cylinders may be arranged as restoring or return cylinders for raising the upper jaw, or as feed cylinders for rapid lowering of the upper jaw in the first portion of its working stroke. This arrangement has the advantage that the compensating cylinders are acted upon by the lower hydraulic pressure prevailing in the return cylinders and the feed cylinders, and may accordingly be designed with smaller dimensions. A considerable saving on materials and costs is accomplished thereby.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is an elevation of a bending press with the upper jaw partially removed and pressure and return cylinders illustrated partly in section,

FIG. 2 is a vertical cross-section through the bending press according to FIG. 1,

FIG. 3 is a flow diagram of one embodiment of a hydraulic driving device for the upper jaw,

FIG. 4 is a flow diagram of a modified embodiment of the hydraulic driving device for the upper jaw,

FIG. 5 is a flow diagram of another embodiment of th hydraulic driving device for the upper jaw, and

FIG. 6 illustrates a modification to the hydraulic driving device according to FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, the frame of the sheet metal working bending press illustrated in FIGS. 1 and 2 consists of two vertical side walls 1 which are rigidly interconnected, at the front by the bearer 2 of the stationary lower jaw 3, and at the rear by means of an upper crossbeam 4, FIG. 2, and of a lower cross-beam 5. A hydraulic thrust cylinder 6 is fastened with its axis vertical on the upper front extremity of each side wall 1 of the machine frame. The upper jaw 7 is displaceably guided for reciprocation in vertical guides 8 which are fastened on the inwardly directed sides of the two thrust cylinders 6. The thrust cylinders 6 are single-acting hydraulic cylinders having an upper pressure space 206, FIG. 1, i.e. situated above the corresponding piston 106. The piston rods 306 of the thrust cylinders 6 extend downwards out of the cylinders 6 and co-operate with lateral steps 107 on the upper jaw 7.

Return cylinders 9 are fastened on brackets projecting from the corresponding side wall 1 of the machine frame and have their axes vertical on the rear side of the upper jaw 7, close to the thrust cylinders 6. The return cylinders 9 are single-acting hydraulic cylinders having a lower pressure space 209, FIG. 1, i.e. situated under the corresponding piston 109. The piston rods 309 of the return cylinders extend upwards out of the return cylinders and co-operate with projections 207 on the upper jaw 7.

The rear upper cross-beam 4 of the machine frame is at least partially arranged as an oil tank T, FIG. 2 for the hydraulic system for driving the upper jaw 7. A first embodiment of the hydraulic driving device is illustrated in FIG. 3. In this embodiment, two pumps P1 and P2 are incorporated, which are driven by means of appropriate electric motors M1, M2, and whose delivery pipes F1, F2 are connected through check or non-return valves R1, R2 to a common feed or delivery pipe 11. The pump P1 is constructed as a low-pressure pump having a high rate of delivery. By contrast, the pump P2 is constructed as a high-pressure pump having a relatively low rate of delivery. The delivery pipe P1 of the low-pressure pump P1 is connected to the oil tank T of the hydraulic system through a branch and an adjustable pressure limiting valve 12.

The hydraulic driving device has two co-axial compensating cylinders 13 which are preferably formed in one unit or are assembled to form a unit A, and the cylinders 13 preferably have the same dimensions, i.e. the same cross-sectional area and the same volume. A compensating piston #113 is displaceably arranged in each compensating cylinder 13. The compensating pistons 113 are firmly interconnected and are secured to a piston rod 413 common thereto and which protrudes ambilaterally from the compensating cylinders 13. The piston rod 413 is of constant diameter throughout. The effective piston areas which may be acted upon by pressure, accordingly have the same size in the case of both compensating pistons 113 as well as at either side of each compensating piston 113.

The pressure spaces 213 (pressure transmission spaces) of the two compenating cylinders, which space are situated at the ame side of the compensating piston 113, e.g. the left-hand side of FIG. 3, are each connected to the pressure spaces 209 of the return cylinders 9 through pipes 14. The pressure spaces .313 (control spaces) of the two compensating cylinders 13 situated at the opposite side, e.g. the right-hand side in FIG. 3, are connected to a switching or reversing valve V,, which is electromagnetically actuated and constructed as a multiway valve, through a pipe 16 common thereto and to a non-return valve R. The connecting pipe 16 is connected at a point, which lies between the compensating cylinders 13 and the non-return valve R, to the oil tank T of the hydraulic system through an adjustable pressure limiting valve 22.

The reversing valve V is connected to the oil tank T and to the common delivery pipe 11 of the two pumps P1, P2, as well as, through a connecting pipe 17 and appro priate branch pipes, to the pressure spaces 206 of the two pressure cylinders 6. The entire hydraulic system, i.e. the pressure spaces 206, 209 of the pressure and return cylinders 6 and 9, the cylinder spaces 213, 313 of the compensating cylinders 13 and the pipes 14, 16, 17 are filled completely with hydraulic oil. Special steps, not illustrated, are taken, periodically or automatically to verify and ensure this complete filling with oil. The reversing valve V can assume three switching positions. In the central or zero position shown in FIG. 3, the pipes 16 and 17 are connected to the compensating cylinders 13 and to the pressure cylinders 6, whereas the common delivery pipe 11 of the two pumps P1, P2 is connected to the oil tank T. Accordingly, this represents an idle or standby position, in which the upper jaw 7 is im mobilised in its momentary position and the pressure fluid conveyed by the pumps P1, P2 flows back into the oil tank T.

For lowering the upper jaw 7 during the working stroke of the bending press, the reversing or switching valve V is placed in its switching position shown at the left in FIG. 3, in which is connects the common delivery pipe 11 of the pumps P1, P2 to the connecting pipe 17 of the pressure cylinders, 6 whilst shutting off the connecting pipe 16 leading to the compensating cylinders 13, or connects the cylinders 13 to the oil tank T for removal of losses by leakage. During the approach motion of the upper jaw 7, i.e. in the first part of the downward stroke of the upper jaw 7, in which the jaw is simply moved downwards, and does not apply any working or deforming pressure, the volume of pressurized oil simultaneously impelled by the two pumps P1, P2 is pumped through the pipes 11. 17 into the pressure spaces 206 of the pressure cylinders 6. The pistons 106 of the pressure cylinders 6 are consequently moved downwards at relatively high speed and with their piston rods 306 push the upper jaw 7 rapidly downwards. As soon as the upper jaw 7 comes into contact with a workpiece on the lower jaw 3 so that it must overcome a greater resistance to exert the required deforming pressure, the oil pressure correlatively rises in the pressure spaces 206 of the pressure cylinder 6 as well as in the pipes 17, 11 and in the delivery pipes F1, P2 of the two pumps P1, P2. The pressure limitation valve 12 responding to this raised pressure opens automatically and connects the delivery pipe P1 of the low-pressure pump P1 to the oil tank T. The hydraulic oil is then pumped into the pressure spaces 206 of the pressure cylinders 6 only by the high-pressure pump P2. in the last part of its downward stroke, in which the deformation of the workpiece is performed, the upper jaw 7 is thus displaced downwards more slowly, but under the higher working pressure required.

The precise parallel guiding of the upper jaw 7, that is the precisely horizontal position of the lower edge of the upper jaw, is assured during the downward displacement by the return cylinders 9 in conjunction with the compensating cylinders 13. During the lowering of the upper jaw 7, the pistons 109 of the return cylinders 9 are displaced downwards by the projections 207 of the upper jaw 7 through the corresponding piston rods 309, and force the hydraulic oil contained in the pressure spaced 209 in the return cylinders 9 into the co-ordinated pressure transmission spaces 213 of the compensating cylinders 13. The pair of compensating pistons 113 is accordingly displaced towards the right in FIG. 3. the hydraulic oil displaced from the opposed control spaces 313 of the compensating cylinders 13 concomitantly flows back into the oil tank T through the pressure limitation valve 22 branching off from the connecting pipe 16, since the non-return valve R closes in this direction of flow. The same counterpressure which in each case exerts the same opposing force on both identically dimensioned compensating pistons 113. is generated in the pipe 16 and in the control spaces 313 of the two compensating cylinders 13 connected thereto. The sum of these two opposing forces must be overcome during the lowering of the upper jaw 7. For as long as the upper jaw 7 is displaced downwards precisely parallel to itself. that is in a precisely horizontal position, the hydraulic pressure in the pressure spaces 209 of both return cylinders 9 and in both the co-ordinated pressure transmission spaces 213 of the compensating cylinders 13 are equal to each other and correspond to the opposed pressure in each of the two opposed control spaces 313 of these cylinders 13. i.e., if the one-right-hand side extremity of the upper jaw 7 encounters a greater external mechanical resistance during lowering, and has its displacement decelerated more powerfully than the other, for example the left-hand side upper jaw extremity, the pressure generated by the piston 109 in the pressure space 209 of the co-ordinated right-hand side return cylinder 9 and in the pressure transmission space 213 of the co-ordinated right-hand side compensating cylinder 13 connected there to, diminishes correlatively. The pressure in the pressure transmission space 213 of the other and for example the left-hand side compensating cylinder 13 which is connected to the return cylinder 9 of the other left-hand side extremity of the upper jaw and which is exposed to a lesser mechanical deceleration or none, rises simultaneously in the same degree. In point of fact, the opposing pressures in the two control spaces 313 of the compensating cylinders 13 remain unchanged and equal to each other, whereas the sum of the opposing forces engendered by these opposing pressures on the pair of compensating pistons 113 must be equal to the sum of the forces generated on the same pair of compensating pistons 113 by the pressures in the return cylinders 9 and in the co-ordinated pressure transmission spaces 213. The downward displacement of the left-hand side extremity of the upper jaw 7 which is exposed to a lesser degree of mechanical deceleration or none, is thus impeded by the raised hydraulic pressure in the pressure space 209 of the co-ordinated return cylinder 9 to the same degree as the downward displacement of the right-hand side extremity of the upper jaw 7 which is decelerated by the increased or incremental external mechanical resistance. The resistances at the two extremities of the upper jaw 7 are thus mutually balanced automatically. Accordingly, the upper jaw moves downwards precisely parallel to itself and oblique positions or jamming in the guides 8 are reliably prevented.

To raise the upper jaw 7, the reversing valve V is placed in its switching position shown at the right in FIG. 3, in which it connects the pressure spaces 106 of the pressure cylinders 6 to the oil tank T and the common delivery pipe 11 of the pumps P1, P2, through the non-return valve R, open in this direction of flow and through the connecting pipe 16 to the control spaces 313 of the compensating cylinders 13. The pair of compensating cylinders 113 is consequently displaced towards the left in FIG. 3 by the delivery pressure of the pumps P1, P2, the hydraulic oil displaced from the opposed pressure transmission spaces 213 of the compensating cylinders 13 flows through the pipe 14 into the pressure spaces 209 of the return cylinders and upwardly displaces the pistons 109 of these cylinders. Consequently, the upper jaw 7 is lifted by the piston rods 309 of the return cylinders 9 through the projections 207. During this upward stroke of the upper jaw 7, the compensating cylinders 13 with the firmly interconnected compensating pistons .113 perform an automatic compensation of the return pressures acting on both extremities of the upper jaw 7, as a function of the external resistances to be overcome, that is to say in inverse manner to that applicable for the lowering of the upper jaw. In point of fact, if the one extremity of the upper jaw encounters a higher external mechanical resistance whilst being raised, the hydraulic pressure increases correlatively in the pressure space 209 of the co-ordinated return cylinder 9 and in the pressure transmission space 213 of the compensating cylinder 13 connected to the same, whereas the pressure in the pressure transmission space 213 of the other compensating cylinder 13 and in the pressure space 209 of the co-ordinated return cylinder 9 decreases to the same degree. The lifting pressures acting in the two return cylinders 9 thus adapt themselves automatically to the external resistances to be overcome. Accordingly, the upper jaw 7 is moved upwards precisely parallel to itself, without oblique positioning or camming in the guides 8. Since the pressure needed to raise the upper jaw 7 is considerably lower than the working or deforming pressure for the trimming or hanging of the workpiece, the pressure limitation valve 12 is closed during the upward displacement of the upper jaw 7 and the compensating cylinders 13 are acted upon by the volume of oil impelled by the two pumps P1, P2. This ensures rapid lifting of the upper jaw 7, the hydraulic oil displaced from the pressure spaces 206 of the pressure cylinders 6 concomitantly flows back into the oil tank T through the pipe 17' and the reversing valve V.

The modified form of embodiment illustrated in FIG. 4 is similar to the embodiment according to FIG. 3, identical parts bearing the same reference numerals. The sole essential difference consists in that the control spaces 313 of the two compensating cylinders 13 are connected through the connecting pipe 16 to the oil-filled space 118 of a hydropneumatic pressure accumulator 18. During the lowering of the upper jaw 7, the hydraulic oil displaced from the control spaces 313 of the compensating cylinders 13 flows into the pressure accumulator 18. The uniform opposed pressure in the control spaces 313 of the compensating cylinders 13 which is required for compensation of the downward displacement of the upper jaw 7 is thus provided by the pressure accumulator 18. In the switching position of the reversing valve V illustrated at the right in FIG. 4 and corresponding to the upward stroke of the upper jaw 7, this valve connects the pressure spaces 206 of the pressure cylinders 6 as well as the common delivery pipe 11 of the two pumps P1, P2 to the oil tank T. The hydraulic return pressure needed to raise the upper jaw is concomitantly supplied by the pressure accumulator 18. The hydraulic oil stored in the pressure accumulator flows back into the control spaces 313 of the compensating cylinders 13 and correspondingly displaces the pair of compensating pistons 113113.

The embodiment according to FIG. 5 is based on the complementary taks of reducing the additional cost for two pumps P1, P2 and two corresponding motors M1, M2 in the hydraulic driving device of the upper jaw 7 by elimination of one pump and of the co-ordinated motor, whilst nevertheless ensuring a rapid approach motion of the upper jaw 7 during the downward stroke thereof. To this end, a single-acting hydraulic feed cylinder 20 is arranged With its axis vertical and with the pressure space 220 situated above the piston 20, is arranged at each lateral extremity of the upper jaw 7. The piston rods 320 of the cylinders 20 project downwards out of the feed cylinders 20 and act on the upper jaw 7 in the direction of a downward displacement thereof. The feed cylinders 20 may concomitantly be arranged as separate and independent structural components and may act direct on the upper jaw 7 with their piston rods 320, in the same manner as the piston rods 306- of the pressure cylinders '6. In the particularly advantageous form of embodiment illustrated, the two feed cylinders 20 are arranged co-axially and above the corresponding pressure cylinders 6, and the piston rods 320 of the feed cylinders 20 are firmly connected to the pistons 106 and to the piston rods 306 of the pressure cylinders 6. The pistons of the feed cylinders 20 have a diameter which is considerably smaller than the diameter of the pistons 106 of the pressure cylinders 6.

In this case too, the hydraulic driving device of the upper jaw 7 has two compensating cylinders 13 combined into a structural unit A, whereof the identically dimensioned pistons 113 are interconnected firmly by means of a common piston rod 413 of constant diameter. The diameter of the pistons of the compensating cylinders 13 is preferably greater than the diameter of the pistons of the feed cylinders 20. The cylinder spaces 213 (pressure transmission spaces) of the two compensating cylinders 13 situated at the same side of the compensating pistons 113, e.g. the left-hand side in FIG. 5, are connected through pipes 21 with the pressure space 220 of a feed cylinder 20 in each case. The cylinder spaces 313 (control spaces) of the two compensating cylinders 13 which are situated at the opposite side of the compensating pistons 113, eg the right-hand side in FIG. 5, are however connected through a common connecting pipe 16 and a non-return valve R to a reversing valve V. At a point situated between the compensating cylinders 13 and the non-return valve R, the pipe 16 is connected to the oil tank T of the hydraulic system through an adjustable pressure limitation valve 22. The pressure spaces 209 of the return cylinders 9 are in communication with the reversing valve V through a common connecting pipe 23. The pressure spaces 206 of the pressure cylinders 6 are connected to the reversing valve V through a common pipe 17 and an isolating valve 25. The isolating valve is pie-controlled by the pressure prevailing between the valve 25 and the reversing valve V in the pipe 17, as indicated by the control pipe 26 shown dash-dotted. The common pipe 17 of the pressure cylinders 6 is connected to the oil tank T through a branch pipe 24 and a non-return valve R3 at a point lying between the pres sure cylinders 6 and the isolating valve 25. This nonreturn valve R3 may be unblocked, i.e. opened, by the pressure prevailing in the common connecting pipe 23 of the return cylinders 9, as indicated by the control pipe 27 shown dash-dotted. Finally, the hydraulic driving device has a single pump P2 driven by the motor M2, which is constructed as a high-pressure pump having a relatively low rate of delivery and whose delievry pipe F2 is in communication with the reversing valve V through a nonreturn valve R2. The reversing valve V has a connection to the oil tank T.

The reversing valve V is constructed as a multiway valve and may assume three switching positions. In the central or zero position, the three pipes 17, 16 and 23 are shut off from the pressure cylinders 6, the compensating cylinders 13 and the return cylinders 9, whereas the delivery pipe F2 of the pump P2 is connected to the oil tank T. To lower the upper jaw 7, the reversing valve V is placed in its switching position illustrated at the left in FIG. 3, in which the connecting pipe 23 of the return cylinders 9 is connected to the oil tank T and the pipes 17 and 16 leading to the pressure cylinders 6 and to the compensating cylinders 13 are connected to the delivery pipe P2 of the pump P2. The isolating valve 25 in the connecting pipe 17 of the pressure cylinders 6 remains closed for the time being, so that the hydraulic oil impelled by the pump P2 is forced through the pipe 16 and the non-return valve R opening in this direction of flow into the co-ordinated control spaces 313 of the two compensating cylinders 13 and correspondingly displacing the pair of compensating pistons, i.e. towards the left in FIG. 5. The oil displaced from the opposed pressure transmission spaces 213 of the compensating cylinders 13 flows through the pipes 21 into the pressure spaces 220 of the feed cylinders 20 and thrusts the pistons 120 of these cylinders downwards. Consequently, the upper jaw 7 is lowered by means of the pistons 106 and the piston rods 306 of the pressure cylinders 6 at a relatively high approach speed corresponding to the smaller diameter of the feed pistons 120 compared to the diameters of the pressure pistons 106 on the one hand and of the compensating pistons 113 on the other hand. The oil concomitantly displaced from the pressure spaces 209 of the re turn cylinders 9 by the pistons 109 of these cylinders which are lowered together with the upper jaw 7 flows back into the oil tank T through the pipe 23, whereas o-il flows on or is drawn into the pressure spaces 206 of the pressure cylinders 6 from the oil tank T through the pipes 24, 17 and the non-return valve R3 opens in this direction of flow. Since the action of pressure on the feed cylinders 20 occurs through the pair of pistons 113113 of the compensating cylinders 13, the upper jaw 7 is lowered precisely parallel to itself, as already described in respect of FIG. 3. in point of fact, if the one extremity of the upper jaw '7 encounters a greater external resistance whilst being lowered, the hydraulic pressure in the pressure transmission space 213 of the co-ordinated compensating cylinder 13 and in the pressure space 220 of the feed cylinder 20 connected to the same increases correlatively, whereas the pressure in the pressure transmission space 213 of the other compensating cylinder 13 and in the pressure space 220 of the coordinated feed cylinder 20 diminishes in the same degree.

When the upper jaw 7 comes into contact with the workpiece at the end of its feed motion and must accordingly overcome a greater resistance to exert the required deforming pressure, the hydraulic pressure increases correlatively in the delivery pipe P2 of the pump P2 and in the connecting pipe 17 of the pressure cylinders 6 connected thereto. The isolating valve 25 pre-controlled by this pressure is opened thereby. Consequently, the delivery pressure of the pump then acts direct on the pressure spaces 206 of the pressure cylinders 6 through the pipe 17 and the isolating valve 25, whereas the non-return valve R3 closes. In the final portion of its downward stroke, the upper jaw 7 is thus lowered more slowly but with the required higher working thrust, by the pistons 106 of the pressure cylinders 6.

To raise the upper jaw 7, the reversing valve V is placed in the switching position illustrated at the right in FIG. 5, in which the connecting pipes 16 and 17 of the compensating cylinders 13 and of the pressure cylinders 6 are connected to the oil tank T, and the connecting pipe 23 of the return cylinders 9 is connected to the oil tank T, and the connecting pipe 23 of the return cylinders 9 is connected to the delivery pipe of the pump P2. The hydraulic oil is then pumped into the pressure spaces 209 of the two return cylinders 9 whose pistons 109] are raised and displace the upper jaw upwards through the piston rods 309 and the entraining projections 207. The pressure built up in the pipe 23 leading to the return cylinders 9 opens the non-return valve R3 through the control pipe 27. The oil displaced from the pressure spaces 106 of the pressure cylinders 6 by the upwardly displaced pressure pistons 106 flows back through the pipe 17 and through the opened non-return valve R3 into the oil tank T. The oil displaced from the pressure spaces 220 of the feed cylinders 20 by the pistons which are conjointly entrained as well, is forced into the pressure transmission spaces 213 of the compensating cylinders 13 connected to the same. The pair of compensating pistons 113 is consequently displaced towards the right in FIG. 5. The hydraulic oil concomitantly displaced from the opposed control spaces 313 of the compensating cylinders 13 flows back into the oil tank T throttgh the pressure limitation valve 22 branching off from the pipe 16, since the non-return valve R closes in this direction of flow. A counter-pressure which assures precisely parallel guiding of the upper jaw 7 during lifting, i.e. prevents oblique positioning and jamming as has already been set forth in respect of FIG. 3, is thus built up in the control spaces 313 of the two compensating cylinders 13. In point of fact, if one extremity of the upper jaw 7 is decelerated more powerfully by a greater mechanical resistance during the upward stroke, the hydraulic pressure decreases correlatively in the pressure space 220 of the coordinated feed cylinder 20 and in the pressure transmission space 213 of the compensating cylinder 13 connected thereto, whereas the hydraulic pressure in the pressure transmission space 213 of the other compensating cylinder 13 and in the pressure space 220 of the other feed cylinder 20 connected to the same increases in the same degree. The upward displacement of the extremity of the upper jaw which undergoes a lesser mechanical deceleration must therefore overcome an increased hydraulic resistance as a result of the pressure rise in the co-ordinated feed cylinder 20. The resistances made up of an external mechanical force and a hydraulic force engendered by the feed cylinders 20, which act on the two extremities of the upper jaw against the upward displacement of the same, are automatically balanced thereby.

The modified embodiment partially illustrated in FIG. 6 differs from the embodiment according to FIG. 5 merely in that the return cylinders 9 are omitted and that, in exchange, the feed cylinders 20 are constructed as doubleacting cylinders. The function of the return cylinders 9 is now taken over by the lower pressure space 420 of the feed cylinders 20, which is connected to the reversing valve V through the pipe 23 and is acted upon by pressure upon raising the upper jaw, no other change intervening in the mode of operation of the hydraulic driving device. In this case however, the piston rods 306 of the pressure cylinders 6 must be tractively linked to the upper jaw 7, or the piston rods 320 of the feed cylinders 20 must also extend upwards out of these and co-operate from below with a projection 207 of the upper jaw 7.

What is claimed is:

1. A hydraulic device for a trimming or like press the hydraulic system of which includes a vertically reciprocable upper jaw and two hydraulic control cylinders disposed in spaced relation and arranged simultaneously to be acted upon by pressure to effect lowering and raising of the upper jaw, comprising by two compensating cylinders each housing a compensating piston, said pistons being firmly interconnected and on sides thereof facing in the same direction having surfaces of equal area to be acted upon by pressure, the compensating cylinder spaces on one side of the compensating pistons each being connected to the pressure space of a displacing of control cylinder and the compensating cylinder spaces at the opposite sides of the compensating pistons being arranged to be acted upon by the same hydraulic counter-pressure or impelling pressure.

2. A device according to claim 1, including two pressure cylinders for lowering the upper jaw and two return cylinders for raising the upper jaw, wherein the pressure transmission spaces of the compensating cylinders are each connected to the pressure space of a return cylinder and the control spaces of the compensating cylinders are connectable during the lowering of the upper jaw to an oil tank in the hydraulic system through a pressure limitation or restricting valve, and during the raising of the upper jaw are connectable to the delivery pipe of an oil pump.

3. A device according to claim 1, including two pressure cylinders for lowering the upper jaw and two return cylinders for raising the upper jaw, wherein the pressure transmission spaces of the compensating cylinders are each connected to the pressure space of a return cylinder, and the control spaces of the compensating cylinders are connected to a hydro-pneumatic pressure accumulator.

4. A device according to claim 1, including two feed cylinders and two pressure cylinders for lowering the upper jaw and two return cylinders for raising the upper jaw, wherein the pressure transmission spaces of the compensating cylinders are each connected to the pressure space of a feed cylinder, and the control spaces of the compensating cylinders are connectable during the lowering of the upper jaw to the delivery pipe of an oil pump, and during the raising of the upper jaw are connectable to an oil tank in the hydraulic system through a pressure limitation or restricting valve.

5. A device according to claim 4, wherein the pressure spaces of the pressure cylinders are connectable upon lowering the upper jaw during rapid downward movement thereof, to the oil tank through a non-return valve opening in the direction of suction, and during a subsequent slower working displacement of the upper jaw are connectable to the delivery pipe of the oil pump through a controlled isolating valve.

6. A device according to claim 5, wherein the isolating valve is controlled by pressure prevailing in the delivery pipe of the oil pump.

7. A device according to claim 5, wherein the non-return valve is arranged to be automatically opened during the raising of the upper jaw by pressure built up in the pressure spaces of the return cylinders.

8. A device according to claim 4, wherein the pistons of the displacing or control cylinders are firmly connected to the pistons of pressure cylinders co-axially therewith.

9. A device according to claim 8, wherein one displacing or control cylinder and one return cylinder are combined into a double-acting hydraulic cylinder.

10. A device according to claim 1, wherein the two compensating cylinders are combined into a structural unit comprising compensating pistons of identical size which are secured to a piston rod of constant diameter common thereto.

References Cited UNITED STATES PATENTS 2,499,563 3/1950 Bill 54.5 UX 2,759,330 8/ 1956 Van Broekhoven et al. 6097 E 3,448,577 6/1969 Crawford 6097 EX EDGAR W. GEOGHEGAN, Primary Examiner U.S. Cl. X.R. 

